During the development of ZenNode, I often wondered what was going on with the BSP structures that were being built. Was this algorithm doing better than that one? How balanced is the tree? How deep is it going? ... BSPInfo grew out of the tool used to see what was going on. It reports statistics to describe the BSP tree. It can be used to give you a feel of how particular Node builders are performing.
The following is a brief description
of each of the values displayed by BSPInfo.
Depth: The maximum depth of the BSP tree. The deeper the tree, the more work DOOM has to do to update the display. A smaller value means that, on average, DOOM will have fewer NODES to traverse when updating the screen.
FOM: (Figure of Merit) This is an attempt to measure the 'balance' of the tree. Each node with both a right and left child or no children is considered balanced. The FOM value is a ratio of balanced nodes to the overall number of nodes.An FOM of 1.000 indicates perfect binary tree. This will *VERY RARELY* occur, since it requires a number of nodes that is a power of 2 and every node being balanced.
Balance: Indicates the percentage of nodes to the left and right of the root node. Generally, a more balanced tree is preferable to a less balanced tree, since, the average depth for any node is likely to be smaller. (This actually is an indication of how well the node builder chose it's first partition.)
Splits: How many times the Node builder had to split segments to fit everything into the tree. There are no hard rules saying that splits are bad, however fewer is generally better.
Diagonals: The number of BSP partition lines chosen that were diagonal. The DOOM rendering engine runs much faster when the partition lines are either vertical or horizontal. Generally the fewer diagonals the better.
Nodes: Number of NODES in the map.
Segs: Number of SEGS in the
map.
IMPORTANT:
None of these figures are meant
to imply that one Node builder is better (or worse) than another.
They are simply designed to describe the type of BSP trees being built.
Some favor shallow tree depths, others attempt to reduce splits, others
favor reducing diagonals. No one value should be viewed as more important
than the others. In general, if a Node builder builds a BSP tree
with all values significantly lower, except FOM, than other Node builders,
it most likely means that that level will play slightly faster in DOOM
but is no more or less 'correct' than any other Node builder. Of
course these numbers aren't important. The only thing that is important
is that the BSP tree created works correctly under DOOM.